Net Energy Balance Research Articles

Sustainable steel through hydrogen plasma reduction of iron ore: Process, kinetics, microstructure, chemistry

Iron- and steelmaking is the largest single industrial CO2 emitter, accounting for 6.5% of all CO2 emissions on the planet. This fact challenges the current technologies to achieve carbon-lean steel production and to align with the requirement of a drastic reduction of 80% in all CO2 emissions by around 2050. Thus, alternative reduction technologies have to be implemented for extracting iron from its ores. The hydrogen-based direct reduction has been explored as a sustainable route to mitigate CO2 emissions, where the reduction kinetics of the intermediate oxide product FexO (wüstite) into iron is the rate-limiting step of the process. The total reaction has an endothermic net energy balance. Reduction based on a hydrogen plasma may offer an attractive alternative. Here, we present a study about the reduction of hematite using hydrogen plasma. The evolution of both, chemical composition and phase transformations was investigated in several intermediate states. We found that hematite reduction kinetics depends on the balance between the initial input mass and the arc power. For an optimized input mass-arc power ratio, complete reduction was obtained within 15 min of exposure to the hydrogen plasma. In such a process, the wüstite reduction is also the rate-limiting step towards complete reduction. Nonetheless, the reduction reaction is exothermic, and its rates are comparable with those found in hydrogen-based direct reduction. Micro- and nanoscale chemical and microstructure analysis revealed that the gangue elements partition to the remaining oxide regions, probed by energy dispersive spectroscopy (EDS) and atom probe tomography (APT). Si-enrichment was observed in the interdendritic fayalite domains, at the wüstite/iron hetero-interfaces and in the oxide particles inside iron. With proceeding reduction, however, such elements are gradually removed from the samples so that the final iron product is nearly free of gangue-related impurities. Our findings provide microstructural and atomic-scale insights into the composition and phase transformations occurring during iron ore reduction by hydrogen plasma, propelling better understanding of the underlying thermodynamics and kinetic barriers of this essential process.

Biorefinery of genetically modified soybean as biodiesel with sustainable production system in Indonesia: A review

Fossil energy consumption in Indonesia is high every year, and this can cause an imbalance between demand and the availability of available fuel. Besides, fossil fuels are also classified as non-renewable fuels, so that the availability of fuel can be used up if exploited continuously. High diesel consumption makes it necessary to search for other energy sources that can be used to meet diesel needs in Indonesia. Alternative diesel replacement that can be used is biodiesel fuel from soybeans. One of the disadvantages of using soy as a biodiesel feedstock is its low oil content. An alternative that can be done is by using genetically modified (GM) soybeans that have higher oil content. The biorefinery approach can also be carried out as an effort to make biodiesel production sustainable, both economically and environmentally. GM soybean can be assembled through several stages, which are selection of varieties, assembly of GM soybean, and then testing and licensing. After that, soybeans can be used and utilized in the Indonesian market. The biodiesel production system from GM soybeans using a biorefinery approach is carried out by utilizing residues during production into other products so that it can be an additional income, and reduce the impact of environmental pollution. A high net energy balance ratio (NER) in some biodiesel production from soybeans makes biodiesel production from soybeans can be said to be renewable and economically sustainable. Biodiesel production from GM soybeans with the concept of biorefinery has the opportunity to become a sustainable industry, both economically and environmentally.

Flight trajectory optimization of sun-tracking solar aircraft under the constraint of mission region

The optimal yawing angle of sun-tracking solar aircraft is tightly related to the solar azimuth angle, which results in a large arc flight path to dynamically track the sun position. However, the limited detection range of payload usually requires solar aircraft to loiter over areas of interest for persistent surveillance missions. The large arc sun-tracking flight may cause the target area on the ground to be outside the maximum coverage area of payload. The present study therefore develops an optimal flight control approach for planning the flight path of sun-tracking solar aircraft within a mission region. The proposed method enables sun-tracking solar aircraft to maintain the optimal yawing angle most of the time during daylight flight, except when the aircraft reverses its direction by turning flight. For a circular region with a mission radius of 50 km, the optimal flight trajectory and controls of an example Λ-shaped sun-tracking solar aircraft are investigated theoretically. Results demonstrate the effectiveness of the proposed approach to optimize the flight path of the sun-tracking aircraft under the given circular region while maximizing the battery input power. Furthermore, the effects of varying the mission radius on energy performance are explored numerically. It has been proved that both net energy and energy balance remain nearly constant as the radius constraint varies, which enables the solar aircraft to achieve perpetual flight at almost the same latitude as the large arc flight. The method and results presented in this paper can provide reference for the persistent operation of sun-tracking solar aircraft within specific mission areas.

Techno-economic perspectives of the temperature management of photovoltaic (PV) power plants: A case-study in Iran

The study aimed at revealing the techno-economic analyses of the temperature management of photovoltaic (PV) modules. For this aim, an existing PV power plant (PP) located in Zanjan, north-west of Iran was analyzed experimentally. Two different cooling scenarios (cases A and B with 3 and 6 low-energy fans per module) were considered. The net energy balance showed that more net electrical energy is produced in case A. The net specific energy (kWh per kWp) could be increased up to 4.4% and 4.1% in July, respectively for cases A and B. The selected cooling system (i.e. case A) was analyzed economically according to three different possible scenarios: considering different feed-in tariff (FiT) rates, change in PV module degradation rates, and increasing the size of a PV PP vs applying the thermal management system. Results revealed that a thermal management system would be economically justifiable only at high FiT rates. Finally, considering the reduction in the degradation rate of PV modules is necessary for economic analyses due to the possible lowering in the pay-back period as up to three years seen in the present study.

ЭФФЕКТИВНОСТЬ ВОЗДЕЛЫВАНИЯ ПИВОВАРЕННОГО ЯЧМЕНЯ НА РАЗНЫХ ФОНАХ МИНЕРАЛЬНОГО ПИТАНИЯ И НОРМАХ ВЫСЕВА

Of the field crops cultivated in Mordovia, the leading position belongs to barley, which is used for food, feed and brewing purposes. The latter option of its use is economically feasible and many varieties are used for these purposes. Knowledge of the influence of individual technology elements (mineral fertilizes and nutritional area) on productivity, economic and energy parametres and grain quality of new intensive type varieties in specific soil and climatic conditions is very important. The experiment was carried out to establish the possible parameters of productivity of malting barley of Grace variety in case of different types of mineral nutrition and plant density, with the task to identify the impact of the studied factors on grain yield and economically and energy efficient variants. Experimental work was carried out on the educational and experimental farm at Ogarev National Research University named after N. P. Ogarev in 2012, 2014 and 2015. The article shows the features of grain yield formation, economic and energy parametres, depending on technology elements. The suitable doses of fertilizers and seeding amount of malting barley cultivation were identified. The results of impact studies of fertilizers and plant density on grain yield and cost; net and energy income, profitability, bioenergy efficiency of Grace malting barley when cultivated on leached black soils of Mordovia are presented. It was found that the highest grain yield (3.84 t / ha), conditional net income (26277 rubles / ha) and energy balance (49.3 GJ / ha) are observed when fertilizing with N60P60K60 and sowing 5.5 million seeds per hectare; with the same planting density, but without fertilizer application - profitability (374 %). The maximum bioenergy efficiency coefficient (4.6) and the minimum grain cost (2214 rubles / ha) were noted with a seeding amount of 5.5 million / ha, but the predominant energy efficiency coefficient (3.0) and the lowest grain energy intensity was 94. 8 GJ / t) - with a seeding amount of 4.0 million / ha

Targeted assessment of the metabolome in skeletal muscle and in serum of dairy cows supplemented with conjugated linoleic acid during early lactation

In the dairy cow, late gestation and early lactation are characterized by a complexity of metabolic processes required for the homeorhetic adaptation to the needs of fetal growth and milk production. Skeletal muscle plays an important role in this adaptation. The objective of this study was to characterize the metabolome in skeletal muscle (semitendinosus muscle) and in serum of dairy cows in the context of the physiological changes occurring in early lactation and to test the effects of dietary supplementation (from d 1 in milk onwards) with conjugated linoleic acids (sCLA; 100 g/d; supplying 7.6 g of cis-9,trans-11 CLA and 7.6 g of trans-10,cis-12 CLA per cow/d; n = 11) compared with control fat-supplemented cows (CTR; n = 10). The metabolome was characterized in skeletal muscle samples collected on d 21 and 70 after calving in conjunction with their serum counterpart using a targeted metabolomics approach (AbsoluteIDQ p180 kit; Biocrates Life Sciences AG, Innsbruck, Austria). Thereby 188 metabolites from 6 different compound classes (acylcarnitines, amino acids, biogenic amines, glycerophospholipids, sphingolipids, and hexoses) were quantified in both sample types. In both groups, dry matter intake increased after calving. It was lower in sCLA than in CTR on d 21, which resulted in reduced calculated net energy and metabolizable protein balances. On d 21, the concentrations of dopamine, Ala, and hexoses in the skeletal muscle were higher in sCLA than in CTR. On d 21, the changed metabolites in serum were mainly long-chain (>C24) diacyl phosphatidylcholine PC (PC-aa) and acyl-alkyl phosphatidylcholine (PC-ae), along with lysophosphatidylcholine acyl (lysoPC-a) C26:1 that were all lower in sCLA than in CTR. Supplementation with CLA affected the muscle concentrations of 22 metabolites on d 70 including 10 long-chain (>C22) sphingomyelin (SM), hydroxysphingomyelin [SM(OH)], PC-aa, and PC-ae along with 9 long-chain (>C16) lysoPC-a and 3 metabolites related to amino acids (spermine, citrulline, and Asp). On d 70, the concentrations of lysoPC-a C18:2 and C26:0 in serum were higher in the sCLA cows than in the CTR cows. Regardless of treatment, the concentrations of Ile, Leu, Phe, Lys, His, Met, Trp, and hydroxybutyrylcarnitine (C4-OH) decreased, whereas those of ornithine, Gln, and trans-4-hydroxyproline (t4-OH-Pro) increased from d 21 to 70 in muscle. The significantly changed metabolites in serum with time of lactation were 28 long-chain (>C30) PC-ae and PC-aa, 7 long-chain (>C16) SM and SM(OH), along with lysoPC-a C20:3 that were all increased. In conclusion, in addition to other significantly changed metabolites, CLA supplementation mainly led to changes in muscle and serum concentrations of glycerophospholipids and sphingolipids that might reflect the phospholipid compositional changes in muscle. The metabolome changes observed in sCLA on d 21 seem to be, at least in part, due to the lower DMI in these cows. The changes in the muscle concentrations of AA from d 21 to 70, which coincided with the steady energy and MP balances, might reflect a shift of protein synthesis/degradation balance toward synthesis.

Net energy, energy utilization, and nitrogen and energy balance affected by dietary pea supplementation in broilers.

Pea starch consists predominantly of C-type of amylopectin chain which is more resistant to digestive enzymes than A-type of starch thus slowly digested in poultry. It was hypothesized that the presence of slowly digested pea starch in broiler diets will increase net energy and the efficiency of energy utilization in broilers. Two experiments were performed to investigate starch digestibility of pea at different incubation times (in vitro study) and the effect of dietary pea on heat increment and net energy in broilers using an open-circuit respiratory calorimetry system (in vivo study). One-day-old Ross 308 male broilers were fed a common starter crumble from d 1 to 10 and standard grower diets thereafter. At d 21, birds were transferred to the chambers each housing 2 birds. Each treatment was replicated 6 times with 2 identical runs of 3 replicates per treatment. A wheat-soybean meal-based diet was used as a control and the treatment diet contained 500 g of pea/kg pea. In vitro study showed that pellet processing increased (P < 0.001) starch digestibility, particularly at shorter times for wheat and a much larger response for pea. Birds offered the pea-based diet had lower (P = 0.002) feed intake, lower (P = 0.020) body weight gain, but a similar (P > 0.05) FCR compared to those offered the wheat-based diet. Net energy (NE) and apparent metabolizable energy (AME) values were higher in the pea-based diet than in the wheat-based diet (P = 0.037 for NE and P = 0.018 for AME). Heat production, respiratory quotient, heat increment of feed, efficiency of utilization of gross energy for AME, and efficiency of utilization of AME for NE did not differ (P > 0.05) between the 2 treatments. There was no effect (P > 0.05) of pea on the total tract digestibilities of dry matter, crude protein and ash, but the total tract digestibility of starch was higher (P = 0.022) in the pea-based diet compared to the wheat-based diet. This study provides insight into the energy metabolism of broilers offered a pea-based diet and indicates that dietary pea supplementation increases dietary AME and NE but has no effect on heat increment of feed and the efficiency of energy utilization in broilers.

Bioenergy recovery from methanogenic co-digestion of food waste and sewage sludge by a high-solid anaerobic membrane bioreactor (AnMBR): mass balance and energy potential

To support smart city in terms of municipal waste management and bioenergy recovery, a high-solid anaerobic membrane bioreactor (AnMBR) was developed for sewage sludge (SeS) and food waste (FW) treatment in this study. COD mass balance showed that 54.1%, 66.9%, 73.5%, 91.4% and 93.5% of the COD input was converted into methane at the FW ratio of 0, 25%, 50%, 75% and 100%, respectively. The corresponding net energy balance was 13.6, 14.1, 17.1, 22.9 and 27.4 kJ/g-VS, respectively. An important finding of this investigation was that, for the first time, the relationship between net energy balance and carbon to nitrogen (C/N) ratio was revealed and the established sigmoid-type function was shown to be capable of predicting energy balance at different C/N ratios regardless of the region. The outcomes of this study show the potential of high-solid AnMBRs in SeS and FW treatment for supporting smart cities in the future.

Net Zero Energy Building (NZEB) Design

Presently, buildings are expected to be designed to meet higher energy performance, sustainability to enjoy healthy and comfortable environment for the occupants. With the growing public awareness of environment issues, the energy efficient design concept for construction of buildings is being accepted to reduce the day-to-day energy demand of the buildings. In this scenario, net zero energy building design is one of the solutions to combat global warming by reducing energy demand and simultaneously use of renewable energy to run the operations of the building. In this paper, the focus is given on net zero energy building design criteria for composite climate zone. The technical parameters of planning, orientation, envelope, heating ventilation and air-conditioning (HVAC), use of energy efficient materials and integration of renewable energy system in designing the net zero energy building were analyzed and evaluated. The net zero energy balance equation was established from the building design strategies by evaluating the total annual energy demand, reduction in annual energy consumption implementing energy efficient technologies and annual renewable energy generation under the boundary of the building. This equation of net zero energy building was validated on design and construction of BISA building located at Ludhiana, Punjab falls under the composite climate zone. The analysis, evaluation and validation were carried out on system-generated model of the building. The reduced annual energy demand of the building of 432,742 kWh was met from the renewable energy generation of rooftop solar photovoltaic power plant of capacity 300kWp and satisfied the net zero energy balance equation.

Urban bio-waste as a flexible source of electricity in a fully renewable energy system

This study proposes a curtailment-minimization model to investigate the potential of urban bio-waste to provide flexible electricity to a wind and solar powered Amsterdam. The transition to solar and wind as primary sources of renewable energy is hampered by their intermittent nature. Being controllable, biomass energy holds the potential of providing both renewable and flexible power. For the transformation from urban bio-waste to electricity, a coupled gasifier and solid oxide fuel cell (SOFC) unit was used. An islanded microgrid for the residential area of Amsterdam was investigated on the basis of an average year, both in terms of weather and electricity consumption. The study aims at finding the optimal sizing of each component to provide sustainable and secure electricity supply. Security of electricity supply was guaranteed by ensuring a net positive daily energy balance while minimizing the total surplus energy to be curtailed during the year. All organic municipal solid waste (MSW) available was used representing 39% of the yearly electricity demand of Amsterdam; PV panels (20%) and wind turbines (41%) covered the remaining share. To this end, optimal PV and wind capacities of 186 MW and 165 MW were estimated, representing respectively 16.9% and 94.0% of the total potential capacity of Amsterdam. In this study, the use of urban bio-waste is proven to bring flexibility to the energy system: using more biomass allows lower curtailment values.

Economics of Biofuel Production: A Case of Sorghum and Pearl Millet in India.

Reduction of fossil fuels at an alarming rate has attracted increasing attention to blending biofuels worldwide. India's energy demand is expected to grow at an annual rate of 4-5 times over the next couple of decades. With self-sufficiency levels in crude oil becoming a distant dream, there is growing interest to look out for alternative fuels and the biofuels are an important option for policy makers in India. In this context, this paper reviews the experiences in India in the last two decades with respect to biofuel cultivation and its impact on land use, environment, and the livelihoods of rural communities. The objective of this paper is to assess the economics of biofuel production using Sorghum and Pearl millet feedstocks in India using a Life Cycle Analysis (LCA) approach. Baseline study was conducted during the year 2013 in the Madhya Pradesh state of India covering five districts and 333 sample farmers to understand the farmers perception about the various issues related to the production of biofuels using Indian staple food crops Sorghum and Pearl millet. Empirical data from the multi-locational trials conducted during the years 2014-2015 and 2015-2016 in farmers' fields was used to conduct the LCA analysis. Sorghum and Pearl millet feedstocks which are rain-fed crops are considered for bioethanol production with different pretreatment methods. Net Energy Ratio (NER), Net Energy Balance (NEB), Net Carbon Balance (NCB), and % Carbon reduction were some of the key parameters used for analysis and the results are evaluated based on the environmental impacts through the Life Cycle Assessment at 5% blending. Findings reveal that, dilute alkali pretreatment process is most energy intensive due to consumption of alkali consumption. Whereas dilute acid pretreatment has higher conversion efficiency than the other pretreatment processes which is due to higher glucan and xylan conversion efficiencies.The study concludes that Sorghum feedstock is more energy intensive than Pearl millet feedstock due to higher water requirement and yield. Biofuels, either conventional or advanced, should not been couraged without a comprehensive outlook on the overall impact that will ultimately have on the society, environment, or on the countries' energy security. Efforts should be made toward encouragement of research and development in the field as well as in formulating a comprehensive and effective biofuel policy for India.

Conjugated linoleic acid (CLA) supplementation effects on performance, metabolic parameters and reproductive traits in lactating Holstein dairy cows.

The objective of the study was to determine the effects of conjugated linoleic acid (CLA) supplement on milk yield and composition, blood metabolites and reproductive parameters in lactating Holstein dairy cows. Twenty Holstein dairy cows were randomly assigned to one of two dietary treatments: 1) supplementing 110 g per day of fat (control), 2) supplementing 120 g per day of rumen-protected CLA. The diets were formulated to be nutritionally isocaloric and isonitrogenous. The experimental period started 21 days pre-calving and continued until 60 days in milk (DIM). Treatments had no effect on dry matter intake (DMI), body weight (BW) and body condition score (BCS). The CLA treatment increased milk yield (3.04 kg per day and milk lactose concentration, but decreased milk fat concentration and, short and medium chain fatty acids concentrations. No treatment differences were observed in milk protein concentration, milk energy output and net energy balance. Serum concentrations of glucose, cholesterol, triglyceride (TG), insulin, insulin-like growth factor-1(IGF-1), estradiol and progesterone were higher in CLA treated cows when compared to cows fed on the control diet. Serum beta-hydroxybutyric acid (BHBA) concentration was reduced in cows fed on the CLA treatment. Days to first insemination and days open were not different between the two treatment groups. Cows fed on the CLA supplement had increased conception rate from the first service. The results indicated that cows fed on diets supplemented with CLA produced milk with decreased milk fat concentration whereas some related cow blood serum metabolic parameters associated with reproductive response were increased and resulted in an increased conception rate from the first service.

AgentSeal: Agent-based model describing movement of marine central-place foragers

Understanding why animals move as they do when searching for resources is a central question in ecology, and a prerequisite for the development of predictive process-based models for conservation and management. Many species are central-place foragers (CPF). While several models for CPFs have been proposed, they often assume well-defined return rules to the focal point (like breeding). For some CPFs, however, the decisions to return to central sites are governed by multiple interactions between environmental and physiological factors.We present AgentSeal, a behaviour- and physiology-based, spatially explicit, agent-based model. We use harbour seals, a marine CPF, as a case study and focus on individuals outside their breeding and moulting seasons to capture general fine- and large-scale movements and drivers behind CPF. We model movement decisions based on optimal foraging strategy, cognitive and physiological processes in a realistic landscape, coupled with realistic prey distribution and tuned to a range of behavioural and physiological patterns observed at different scales and levels of organisation (pattern-orientated modelling, POM).The model can reproduce energetic, movement and other behavioural patterns such as net energy balance, at-sea and on land site fidelity, daily activity budgets and trip extents. The model reveals the crucial elements needed to model return-trips of CPFs including movement characteristics that vary as a function of local environmental conditions, cognitive mapping of foraging areas as points of attraction in subsequent foraging trips, and physiological requirements defining switches between resting and foraging.We discuss potential applications and extensions of the model, including investigations of fundamental questions in foraging ecology: how spatial distribution and aggregation of resources affect movement of marine CPFs; what are the main drivers behind their at-sea site-fidelity to foraging patches? We also discuss applied objectives such as improving our understanding of population-level consequences of anthropogenic disturbances and ultimately evolving AgentSeal into a practical management tool.

The effects of food supply on reproductive hormones and timing of reproduction in an income-breeding seabird

Current food supply is a major driver of timing of breeding in income-breeding animals, likely because increased net energy balance directly increases reproductive hormones and advances breeding. In capital breeders, increased net energy balance increases energy reserves, which eventually leads to improved reproductive readiness and earlier breeding. To test the hypothesis that phenology of income-breeding birds is independent of energy reserves, we conducted an experiment on food-supplemented (“fed”) and control female black-legged kittiwakes (Rissa tridactyla). We temporarily increased energy costs (via weight handicap) in a 2 × 2 design (fed/unfed; handicapped/unhandicapped) during the pre-laying period and observed movement via GPS-accelerometry. We measured body mass, baseline hormones (corticosterone; luteinising hormone) before and after handicap manipulation, and conducted a gonadotropin-releasing hormone challenge. Females from all treatment groups foraged in similar areas, implying that individuals could adjust time spent foraging, but had low flexibility to adjust foraging distance. Consistent with the idea that income breeders do not accumulate reserves in response to increased food supply, fed birds remained within an energy ceiling by reducing time foraging instead of increasing energy reserves. Moreover, body mass remained constant until the onset of follicle development 20 days prior to laying regardless of feeding or handicap, implying that females were using a ‘lean and fit’ approach to body mass rather than accumulating lipid reserves for breeding. Increased food supply advanced endocrine and laying phenology and altered interactions between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis, but higher energy costs (handicap) had little effect. Consistent with our hypothesis, increased food supply (but not net energy balance) advanced endocrine and laying phenology in income-breeding birds without any impact on energy reserves.

Catalysis Deoxygenation and Hydrodeoxygenation of Edible and Inedible Oil to Green Fuel

Green diesel or known as the hydrocarbons (alkane and alkene) is a renewable and globally friendly biofuel which generally was derived from the triglycerides or fatty acids. The sustainability of the green diesel always concerned the cost of the production, energy supply and demand (net energy balance), the sustainability of more significant crops production or feedstock supply, acceptance of the country and economic stability. Above all, the lack of the petroleum products, the increase in fuel efficiency and affordable by the public are significant reasons for the green diesel to become one of the most important energy supplies for our future The review found important research areas to be reduction in cost of production and maintenance, improvement in fuel quality and improvement in the environmental benefit from using green diesel. With regard to cost reduction, experiments have been conducted on use of low cost catalysts, waste products as feedstocks and H2-free reaction atmosphere. Fuel quality improvement studies have proposed new catalysts, reaction pathways and conditions to improve hydrocarbon selectivity and fuel stability. Future studies must specifically focus on commercial feasibility of the use of waste materials as feedstocks, heterogeneous catalysts, improvement in reaction pathways to production green diesel and similar other concerns. This article covers the catalysis for deoxygenation, the factor influencing the deoxygenation process and the recent progress of deoxygenation.

Milk 13C and 15N discriminations as biomarkers of feed efficiency and energy status in early lactation cows

Measuring feed utilization efficiency (FUE, milk production / feed intake) and energy status of dairy cows is essential to optimize dairy management and reduce feed waste, but FUE measurement is laborious and costly for dairy farms, particularly when cows are fed in groups. Our study was to investigate whether milk 13C and 15N stable isotope discriminations (naturally existing isotope; milk δ13C or δ15N – diet δ13C or δ15N) were used as biomarkers to estimate FUE, energy balance, and milk production of early lactation cows. Ten multiparous lactating cows with similar body weight (mean ± SD; 691 ± 18.0 kg) and parity (1.6 ± 0.5) were fed a homogeneous diet from 4 to 11 wk postpartum. Body fat had 1.5‰ less δ13C (P < 0.001) and muscle had similar δ13C compared to animal diet. Muscle had more than 2‰ greater δ15N than the diet (P < 0.0001). Milk 13C discrimination was reduced (P = 0.04) and milk 15N discrimination was increased (P < 0.0001) as lactation progressed postpartum. In early lactation, milk 13C discrimination was positively correlated with net energy balance (NEl) (linear; R2 = 0.49), and milk 15N discrimination was negatively correlated with NEl balance (linear; R2 = 0.56). Meanwhile, milk 13C discrimination was negatively and linearly (R2 = 0.30) correlated with feed carbon utilization efficiency, and milk 15N discrimination was positively and linearly (R2 = 0.55) correlated with feed nitrogen utilization efficiency. For milk production, milk 13C discrimination was negatively and linearly correlated with the milk yield (R2 = 0.44), milk fat yield (R2 = 0.40) and lactose yield (R2 = 0.46). Milk 15N discrimination was positively and linearly correlated with the milk protein yield (R2 = 0.49). Collectively, our data revealed that milk 13C and 15N discriminations could be as biomarkers to estimate the FUE, energy status, and milk production of early lactating cows. Potentially, measuring milk isotopic discrimination may be also applied to understand energy and nutrient partitioning of internal C and N reservoirs (body fat and muscle) for supporting milk synthesis in early lactation.

Potential for co-disposal and treatment of food waste with sewage: A plant-wide steady-state model evaluation

The water, food and energy nexus is a vital subject to achieve sustainable development goals worldwide. Wastewater (WW) and food waste (FW) from municipal sources are the primary contributors of organic waste from cities. Along with the loss of these valuable natural resources, their treatment systems also consume a considerable amount of abiotic energy and resource input and make a perceptible contribution to global warming. Hence, the global paradigm has evolved from simple pollution mitigation to resource recovery systems. In this study, the prospects of FW co-disposal into the sewer system and treatment with municipal sewage were quantitatively investigated for Hong Kong's largest biological WW treatment plant (WWTP) by integrated plant-wide steady-state modelling (PWSSM) and lifecycle assessment (LCA) approaches. The investigation assessed the impacts on the design and operational capacity of the WWTP, effluent quality, sludge output, and its net energy and carbon footprint. The results revealed that even at a higher than normal FW to sewage ratio, the WWTP's organic load capacity and performance in terms of organics and nitrogen removal was not significantly degraded, in fact the denitrification efficiency was improved by the FW organics with low N/C ratio. The net energy balance was improved by 80-400%, the net carbon footprint was lowered by 37-63% (without biogenic emissions), while the sludge production was increased by ∼33%. The results are very sensitive and improved with greater influent FW concentration and solids capture in the primary settling unit of the WWTP. The differences in the results have to be seen in relation to uncontrolled methane emission and a faster filling rate if the FW were disposed to landfill. The study provides valuable insights and policy guidelines for the decision makers locally and a generic methodological template.

Trade-Offs in Net Life Cycle Energy Balance and Water Consumption in California Almond Orchards

Perennial cropping systems, such as almond orchards and vineyards, increasingly dominate California’s agricultural landscape. In California’s leading agricultural region, the Central Valley, woody perennials comprise about half of total farmland. Woody perennial orchards produce high value food crops such as almonds, but also generate significant woody biomass which, where feasible, is used to generate biomass-derived electricity. Because of its semi-arid climate, California agriculture is heavily dependent on irrigation, which in some regions, requires energy-intensive pumping processes for both surface and groundwater. This research study explores the tradeoffs in economic, energy and water efficiency, considering the response of almond orchards to water application rates, using a life cycle basis for calculations and considering water scarcity, to reveal one part of the food-energy-water nexus. Findings indicate economic efficiency, represented by business-as-usual practices by growers, and which prioritizes almond yield, does not correspond to the lowest net-energy consumption (i.e. energy consumption minus bioenergy production). Bioenergy production follows a parabolic relationship with applied water, due to almond yield and growth response to water availability. Thus, the net energy footprint of almond production is minimized at about −45% of business-as-usual applied water, at odds with the economic demands of the almond industry that prioritize high value food production.

A multi-level biogas model to optimise the energy balance of full-scale sewage sludge conventional and THP anaerobic digestion

Abstract Anaerobic digestion (AD) is a long-established method for treating wastewater sludge and has been extensively researched, but there remains a lack of generic or practical modelling tools to guide operators and maximise the energy output. Detailed kinetic models have been developed, but are too complex as practical tools for industrial level application. A multi-level model of biogas yield (BY) was therefore developed based on operational data from 72 full-scale sites in the UK showing a wide range of AD performance. The model focused on the controllable operational parameters that are currently monitored at full-scale, including: temperature, hydraulic retention time and dry solids content in the feed sludge. The model effectively described performance variations in BY of full-scale processes, and provides a practical management tool to aid decision support to improve AD efficiency and net energy balance.

A Net Energy Analysis of the Global Agriculture, Aquaculture, Fishing and Forestry System

The global agriculture, aquaculture, fishing and forestry (AAFF) energy system is subject to three unsustainable trends: (1) the approaching biophysical limits of AAFF; (2) the role of AAFF as a driver of environmental degradation; and (3) the long-term declining energy efficiency of AAFF due to growing dependence on fossil fuels. In response, we conduct a net energy analysis for the period 1971–2017 and review existing studies to investigate the global AAFF energy system and its vulnerability to the three unsustainable trends from an energetic perspective. We estimate the global AAFF system represents 27.9% of societies energy supply in 2017, with food energy representing 20.8% of societies total energy supply. We find that the net energy-return-on-investment (net EROI) of global AAFF increased from 2.87:1 in 1971 to 4.05:1 in 2017. We suggest that rising net EROI values are being fuelled in part by ‘depleting natures accumulated energy stocks’. We also find that the net energy balance of AAFF increased by 130% in this period, with at the same time a decrease in both the proportion of rural residents and also the proportion of the total population working in AAFF—which decreased from 19.8 to 10.3%. However, this comes at the cost of growing fossil fuel dependency which increased from 43.6 to 62.2%. Given the increasing probability of near-term fossil fuel scarcity, the growing impacts of climate change and environmental degradation, and the approaching biophysical limits of global AAFF, ‘Odum’s hoax’ is likely soon to be revealed.